1. Technical Field
This disclosure relates to an image forming apparatus that discharges liquid droplets.
2. Description of the Related Art
An image forming apparatus such as a printer, a facsimile machine, a copier, or a multifunction machine may use a liquid discharge apparatus including a recording head that is made up of liquid discharge heads that discharge droplets of recording liquid for applying recording liquid (also referred to as ‘ink’ hereinafter) on a recording medium (also referred to as ‘paper’, ‘paper sheet’, ‘transfer material’, or ‘recording paper’ hereinafter) while conveying the recording medium to form (record/print) an image, for example.
It is noted that in the following descriptions, the term ‘image forming apparatus’ may be used to refer to any apparatus that is configured to discharge liquid on a recording medium of any suitable material such as paper, textile, fiber, fabric, leather, metal, plastic, glass, wood, or ceramic to form an image thereon. Also, the term ‘image forming’ is used to refer to forming (applying) any type of image on a recording medium including an image having meaning such as characters and graphics as well as an image having no meaning such as a pattern. Also, the recording liquid may be any suitable liquid that may be used to form an image on a recording medium and is not limited to ink. Also, the term ‘liquid discharge apparatus’ is used to refer to any apparatus that discharges liquid from a liquid discharge head.
It is noted that an image forming apparatus that uses such a liquid discharge apparatus for forming an image may be in various configurations. For example, the image forming apparatus may have a head tank (also referred to as sub tank or buffer tank) arranged on a carriage as a second liquid accommodating container for accommodating a small amount of recording liquid (ink) to be supplied to the recording head and a large-capacity main cartridge (main tank) arranged at the apparatus main frame side as a first liquid accommodating container so that ink may be supplied to the head tank from the main cartridge arranged at the apparatus main frame side. As another example, the image forming apparatus may have an ink cartridge as a liquid accommodating container that can be exchanged along with a recording head.
In an image forming apparatus that uses a conventional head tank, a flexible resin tube is often used as a supply path for supplying ink from the main tank to the head tank in consideration of wiring within the apparatus, assembling facility, and safety, for example. Also, when negative pressure generating means is arranged within the head tank, an elastic film is often used. However, in such a case, air from the outside may gradually permeate through the film over time to thereby cause air to eventually penetrate into the head tank. Further, air residing in the main tank, air that enters the supply path of the main tank upon its attachment/detachment, or air that is dissolved in the ink may be carried via the ink supply path to eventually end up being accumulated in the head tank.
In this respect, Japanese Laid-Open Patent Publication No. 2006-068904 discloses arranging an outward ink tube for sending ink from the main tank towards the liquid discharge head and a homeward ink tube that extends from the liquid discharge head to the main tank so that air bubbles accumulated in the outward ink tube may be discharged from an air release unit arranged within a sub tank that is disposed between the liquid discharge head and the homeward ink tube.
Also, Japanese Patent No. 3181138 discloses connecting a sub tank to the atmosphere, utilizing the hydraulic head difference between the sub tank and the main tank to redirect ink within the sub tank back to the main tank, and then re-supplying a predetermined amount of ink to the sub tank to remove air bubbles.
Also, Japanese Laid-Open Patent Publication No. 11-320901 discloses opening a valve arranged at a sub tank when a suction head connected to a tubing pump arranged at the image forming apparatus comes into contact with the valve, and discharging air within the sub tank by driving the tubing pump while the valve is opened in the above-described manner.
However, the configuration disclosed in Japanese Laid-Open Patent Publication No. 2006-068904 requires an outward ink tube and a homeward ink tube for each color so that wiring and assembly of the apparatus may become complicated and costs may be raised.
Also, the configuration disclosed in Japanese Patent No. 3181138 that uses the hydraulic head difference to cause ink within the sub tank to flow back to the main tank may require a relatively long processing time. Further, with this configuration, problems may occur in a case where the main tank is exchanged to a new main tank and is left without being used for a long time. That is, since the new main tank is full, ink within the sub tank may not be able to flow back to the main tank so that air bubbles penetrating into the supply path cannot be removed.
Also, the configuration disclosed in Japanese Laid-Open Patent Publication No. 11-320901 that arranges the suction head for discharging air within the sub tank to come into contact with or be detached from the valve arranged within the sub tank, the apparatus structure may be complicated and the air bubble discharging effect may be degraded when the seal of the contacting portions is weak.